The SIG Sauer P320 is a modular semi-automatic pistol made by SIG Sauer, Inc. of Exeter, New Hampshire, and SIG Sauer GmbH of Eckernförde, Germany. It is a further development of the Gun  utilizing a striker-fired mechanism in lieu of a double action only hammer system. The P320 can be chambered in 9×19mm Parabellum, .357 SIG, .40 S&W, and .45 ACP, and can be easily converted from one caliber to another—a change from .357 SIG to .40 S&W requires only a barrel change; a change between 9mm to .357 SIG or .40 S&W and vice versa are accomplished using a caliber exchange kit.

ALSO

The P320 chambered in 9×19mm Parabellum was introduced in the North American market on 15 January 2014, followed by the .45 ACP compact model at the SHOT Show in January 2015.^[2] On 19 January 2017, it was announced that a customized version of the gun had won the United States Army‘s XM17 Modular Handgun System competition. The full-sized model will be known as the M17 and the carry-sized model will be known as the M18.^[3]